Optical pressure sensor assembly

ABSTRACT

Optical pressure sensor assemblies that can be used with existing catheters and imaging systems. Pressure sensors may be compatible with atherectomy and occlusion-crossing catheters, where intravascular pressure measurements at various vessel locations are needed to determine treatment efficacy. The pressure sensors may employ an optical pressure measurement mechanism using optical interferometry, and may be integrated with existing imaging modalities such as OCT. The pressure sensor assemblies may include a movable membrane that deflects in response to intravascular pressure; an optical fiber that transmits light to the movable membrane and receives light reflected or scattered back from the movable membrane into the fiber; and a processor or controller configured to determine the distance traveled by the light received in the fiber from the movable membrane, where the distance traveled is proportional to the intravascular pressure exerted against the membrane.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 14/776,748 filed on Sep. 15, 2015, entitled “OPTICAL PRESSURESENSOR ASSEMBLY,” now U.S. Pat. No. 10,932,670, which is a nationalphase application under 35 USC 371 of International Patent ApplicationNo. PCT/US2013/032011, filed on Mar. 15, 2013, entitled “OPTICALPRESSURE SENSOR ASSEMBLY,” each of which is herein incorporated byreference in its entirety.

This patent application may be related to one or more of the followingpending patent applications: U.S. patent application Ser. No.12/790,703, entitled, “OPTICAL COHERENCE TOMOGRAPHY FOR BIOLOGICALIMAGING,” filed May 28, 2010; U.S. patent application Ser. No.12/829,267, entitled, “CATHETER-BASED OFF-AXIS OPTICAL COHERENCETOMOGRAPHY IMAGING SYSTEM,” filed Jul. 1, 2010; International PatentApplication entitled, “OPTICAL COHERENCE TOMOGRAPHY WITH GRADED INDEXFIBER FOR BIOLOGICAL IMAGING” filed concurrently; U.S. patentapplication Ser. No. 13/433,049, entitled “OCCLUSION-CROSSING DEVICES,IMAGING, AND ATHERECTOMY DEVICES,” filed Mar. 28, 2012; InternationalApplication entitled “OCCLUSION-CROSSING DEVICES” filed concurrently;International Application entitled, “CHRONIC TOTAL OCCLUSION CROSSINGDEVICES WITH IMAGING” filed concurrently; U.S. patent application Ser.No. 12/829,277, entitled, “ATHERECTOMY CATHETER WITHLATERALLY-DISPLACEABLE TIP,” filed Jul. 1, 2010; U.S. patent applicationSer. No. 13/175,232, entitled, “ATHERECTOMY CATHETERS WITHLONGITUDINALLY DISPLACEABLE DRIVE SHAFTS,” filed Jul. 1, 2011; U.S.patent application Ser. No. 13/654,357, entitled, “ATHERECTOMY CATHETERSAND NON-CONTACT ACTUATION MECHANISM FOR CATHETERS,” filed Oct. 17, 2012;U.S. patent application Ser. No. 13/675,867, entitled“OCCLUSION-CROSSING DEVICES, ATHERECTOMY DEVICES, AND IMAGING,” filedNov. 13, 2012; International Patent Application entitled, “ATHERECTOMYCATHETERS WITH IMAGING” filed concurrently; International PatentApplication entitled, “BALLOON ATHERECTOMY CATHETERS WITH IMAGING” filedconcurrently and International Patent Application entitled, “ATHERECTOMYCATHETER DRIVE ASSEMBLIES” filed concurrently. Each of these patentapplications is herein incorporated by reference in its entirety.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

FIELD

Described herein are optical pressure sensing/sensor assemblies formeasuring physiological parameters such as blood pressure and fractionalflow reserve (FFR) in the peripheral and coronary vasculature. Inparticular, the optical pressure sensors and assembly use opticalinterferometry to calculate intravascular pressure. The describedembodiments are compatible for use with existing imaging systems such asoptical coherence tomography and can be used with atherectomy or otherocclusion-crossing devices.

BACKGROUND

Assessing the pressure gradient across a portion of a patient'svasculature provides invaluable information regarding the existence of astenotic lesion or other occlusion that necessitates surgical or othermedical intervention. For example, peripheral artery disease (PAD)affects millions of people in the United States alone. PAD is aprogressive narrowing of the blood vessels most often caused byatherosclerosis, the collection of plaque or a fatty substance along theinner lining of the artery wall. Over time, this substance hardens andthickens, which may interfere with blood circulation to the arms, legs,stomach and kidneys. This narrowing forms an occlusion, completely orpartially restricting flow through the artery. Blood circulation to thebrain and heart may be reduced, increasing the risk for stroke and heartdisease. Similarly, coronary artery disease (CAD) is a narrowing orblocking of blood vessels that supply oxygen to the heart, which if leftuntreated can lead to severe life-threatening or painful conditionsincluding angina pectoris, ischemic necrosis, or myocardial infraction.

Interventional treatments for PAD or CAD may include procedures forwidening vessel lumens or clearing blockages. Endarterectomy is surgicalremoval of plaque from the blocked artery to restore or improve bloodflow. Endovascular therapies such as atherectomy are typically minimallyinvasive techniques that open or widen arteries that have becomenarrowed or blocked. Other treatments may include angioplasty to openthe artery. For example, a balloon angioplasty typically involvesinsertion of a catheter into a leg or arm artery and positioning thecatheter such that the balloon resides within the blockage. The balloon,connected to the catheter, is expanded to open the artery. Surgeons maythen place a wire mesh tube, called a stent, at the area of blockage tokeep the artery open.

Although interventional treatments can be beneficial in managing andtreating PAD or CAD, these treatments can also be completely ineffectivewhere the occlusion is not severe enough to warrant intervention. Wherea lesion is not large enough to substantially affect blood flow,atherectomies, stenting, or other occlusion removal treatments do notprovide any overall benefit to the patient. Rather, employing thesemethods results in over-treating vessels without any commiserateimprovement in the patient's condition.

One way to avoid over-treatment is to assess the pressure changes acrossan occlusion prior to treatment. If the pressure changes satisfy athreshold value, then the patient is a candidate for interventionalprocedures. Typically, referring to FIG. 1 , pressure gradients across aportion of a vessel structure are determined by measuring a firstpressure P1 at a first location on one side of a target treatment siteand a second pressure P2 at a second location on the other end of thetarget treatment site. P1 and P2 are compared. In a healthy vessel, P1and P2 should be approximately the same. However, in an obstructed ornarrowed vessel, P1 is greater than P2 as the pressure increases asblood is forced to move through a narrowed cross-section.

Generally, P1 and P2 are compared by calculating a ratio relating thetwo. For example, in coronary vessels, the fractional flow ratio (FFR)may be calculated to assess whether a blockage is severe enough toactually limit blood flow to the heart. FFR is calculated by FFR=P1/P2.In some cases, the FFR calculation formula is shown, in the art, asPd/Pa, where Pd is the pressure distal to the blockage (e.g. P1) and Pais the pressure proximal to the blockage (P2). Regardless of thenotation using distal or proximal, the concept is the same. The ratiocompares the pressure at one location with another to determine thepressure differential across the target treatment section. A similarcalculation can be used for any vessel to determine a pressure ratio.

Once the pressure gradient or ratio is determined, this value can becompared to an index indicating a threshold value at or above whichinterventional treatment is beneficial. For example, where the FFR isgreater than 0.75, the blockage may be considered severe enough to limitblood flow and should be opened. In other cases, pressure ratios below acut-off indicate that treatment is not warranted and would notsignificantly improve the patient's condition.

In addition to helping establish a course of treatment, pressuremeasurements during procedures also provide immediate feedback onefficacy. Pressure measurements may be taken during an atherectomy todetermine whether the vessel has been widened enough to provide adequateblood flow through the lumen. This prevents over-cutting or excessiveremoval of tissue from the treatment site once pressure measurementsreach a satisfactory range. Likewise, the pressure measurements providefeedback on the need for additional tissue excision where the pressureis still outside acceptable values.

Despite the advantages of having pressure readings, measuringintravascular pressure is challenging with available sensors. One reasonfor this is the dependence on electrical pressure sensors such aselectrical pressure transducers. Electrical sensors operate by measuringelectrical characteristics such as resistance or current flow induced bypositive pressure acting on the sensor (e.g. movement of a sensordiaphragm to increase or decrease electrical resistance). A significantdrawback of this type of sensor is calibration drift or electricalinterference. The sensitivity of electrical sensors is susceptible toenvironmental disturbances such as changing temperature, which affectaccuracy. Accordingly, there is a need for an optical pressure sensorthat avoids these electrical interferences such as drift.

An additional challenge has been the ease of using pressure sensors withexisting atherectomy, occlusion-crossing devices, or vessel imagingsystems (e.g. optical coherence tomography). Because these devices aredesigned to be introduced into and advanced through a patient's narrowvasculature, it is often challenging to include additional componentsfor a pressure sensor without detracting from the optimal size of thedevices. Moreover, the mechanisms of pressure measurement for existingsensors are often independent or incompatible with imaging modalities(e.g. OCT) utilized on devices. As such, there is a need for an opticalpressure sensor that is easily integrated or incorporated into existingvascular treatment devices.

Embodiments described herein address at least these concerns. Inparticular, contemplated embodiments provide for optical pressuresensors and sensor assemblies that can be used alone or in conjunctionwith existing PAD or CAD treatment systems.

SUMMARY OF THE DISCLOSURE

The present invention relates to optical pressure sensing devices,systems, and methods.

Some embodiments described herein provide for an optical pressure sensorassembly, having an optical fiber; a housing having a first end and asecond end, the housing including a lumen through which the opticalfiber extends, the housing having an opening at the first end; anelastic membrane attached to the housing and positioned at the opening,the elastic membrane configured to be movable relative to the housing inresponse to pressure; and an optical fiber connector attached to aproximal end of the fiber, the connector configured for opticalcommunication with a light source.

In some embodiments, a distal end of the optical fiber is secured in thehousing near the opening, the distal end of the fiber may be configuredto transmit light from a light source to the elastic membrane and toreceive light reflected or scattered by the elastic membrane. Inadditional embodiments, the optical fiber is moveable relative to thehousing.

In any of the preceding embodiments, the elastic membrane is adapted todeflect toward the optical fiber under positive pressure. In some of theembodiments, the elastic membrane includes a convex surface facing theoptical fiber when the membrane is deflected under positive pressure. Inany of the preceding embodiments, the elastic membrane is configured tocover the opening.

In any of the preceding embodiments, the elastic membrane is adapted toreflect and scatter light toward a distal end of the optical fiber. Inany of the preceding embodiments, the elastic membrane is made fromfluorinated ethylene propylene.

In any of the preceding embodiments, the elastic membrane includes afirst surface facing the optical fiber and a second surface facing anintravascular lumen, the distance between the first surface and theoptical fiber decreasing when positive pressure is applied to the secondsurface of the elastic membrane. In any of the preceding embodiments,the elastic membrane is adapted to move toward a central longitudinalaxis of the housing under positive pressure.

In any of the preceding embodiments, the pressure sensor device orassembly includes a memory storage device storing pressure sensorcalibration data. The storage device may be an EEPROM storing pressuresensor calibration data for the assembly. In any of the precedingembodiments, the calibration data includes a pressure to deflectionrelationship for the elastic membrane. In any of the precedingembodiments, the pressure sensor device or assembly includes a mirroraligned with the opening to reflect light exiting the fiber toward theelastic membrane.

Any of the preceding embodiments may include an interface medium at thedistal end of the optical fiber, the interface medium having a firstrefractive index different from a second refractive index of the opticalfiber, wherein the differing refractive indices creates a Fresnelreflection. In some embodiments, the interface medium is an adhesivesuch as Masterbond EP42HT-2, EpoTek OG127-4 or OG116, or UV curablephotonics adhesive OP-4-20658.

Any of the preceding embodiments may include a rotational mechanismconfigured to rotate a portion of the assembly to generate an OCT image.

In any of the preceding embodiments, a catheter may form the housing andthe catheter may have an outer diameter of about 0.14 inches to about0.19 inches. In any of the preceding embodiments, a catheter may formthe housing and the catheter may have an outer diameter of about 0.014inches to about 0.019 inches.

In any of the preceding embodiments, the optical connector includes alens configured to transmit collimated light into a proximal end of thefiber.

In any of the preceding embodiments, the assembly is dimensioned forinsertion through a catheter lumen.

Other embodiments provide for an optical pressure sensor system forsensing intravascular blood pressure including a pressure wire assemblyhaving an elongate hollow body having a proximal end and a distal end, atip portion located at the distal end; an opening on the tip portionformed through a wall of the elongate hollow body; an optical fiberextending through the elongate body, the fiber having a light emittingdistal end and a proximal end having an optical connector; and aflexible membrane at the opening, the membrane adapted to move underpressure; and an optical imaging system having a controller, a lightsource, and a detector, the light source in optical communication withthe fiber and the detector configured to receive light reflected orscattered by the membrane. In any of the preceding embodiments, thepressure wire assembly is adapted to measure a pressure exerted on anouter surface of the membrane. In any of the preceding embodiments, thepressure wire assembly is configured to generate a Fresnel referencelight.

In any of the preceding embodiments, the controller may be configured tooperate the detector and control the transmission of light from thelight source. In some variations, the controller is in electricalcommunication with an optical switch, the optical switch configured tomove between at least two modes, one of the modes providing opticalcommunication from the light source through the optical switch and intothe optical connector on the proximal end of the fiber. In some cases,the controller is configured to generate a pressure value for thepressure exerted on the outer surface of the membrane, the pressurevalue generated based on the movement of the flexible membrane inresponse to the pressure exerted on the outer surface the membrane.

In any of the preceding embodiments, the detector receives aninterference signal resulting from the interaction of the Fresnelreference light and light reflected or scattered by membrane. In any ofthe preceding embodiments, the controller receives the interferencesignal from the detector and computes a pressure measurement based onthe interference signal. In any of the preceding embodiments, thecontroller receives the interference signal from the detector andcomputes a pressure measurement based on the interference signal and adeflection-to-pressure relationship for the membrane. In any of thepreceding embodiments, the controller computes a pressure value based ona distance between the fiber distal end and the membrane.

Any of the preceding embodiments may include an intravascular catheterdevice having a hollow shaft adapted for insertion into a blood vessel,the pressure wire assembly dimensioned for insertion through the hollowshaft. In some embodiments, the pressure wire assembly has an outerdiameter between about 0.014 inches to about 0.019 inches. In someembodiments, the pressure wire assembly has an outer diameter betweenabout 0.14 inches to about 0.19 inches.

In any of the preceding embodiments, the pressure wire assembly includesan interface medium at the distal end of the fiber, the interface mediumhaving a first refractive index different from a second refractive indexof a fiber core in the optical fiber.

Other embodiments provide a pressure measurement system having anoptical radiation source; a pressure probe, the probe having an opticalfiber; a housing surrounding a portion of the optical fiber, a distalend of the fiber positioned at an opening of the housing at a first endof the housing; a resilient sheath overlaid across the opening in thehousing, the sheath adapted to deflect in response to a pressure exertedon an outer surface of the sheath, the optical fiber configured totransmit optical radiation to the sheath and receive optical radiationreflected or scattered by the sheath while the sheath is deflected; andan optical connector in optical communication with an optical radiationsource. The pressure measurement system may include receivingelectronics to receive reflected or scattered optical radiation from theoptical fiber and a processor configured to compute a pressure valuebased upon the optical radiation received by the receiving electronics.

Any of the preceding embodiments may include a display in communicationwith the processor, the display configured for displaying measuredpressure values.

In any of the preceding embodiments, the resilient sheath is a flexiblemembrane adapted to deflect toward the optical fiber under positivepressure from the environment. In any of the preceding embodiments, theoptical fiber is removable from the housing.

In any of the preceding embodiments, the resilient sheath is a flexiblemembrane having a convex surface facing the optical fiber when deflectedby pressure exerted on the outer surface.

In any of the preceding embodiments, the processor is configured togenerate the pressure value by comparing the optical radiation receivedby the receiving electronics with a set of pressure calibration data forthe probe.

Any of the preceding embodiments may include a memory storage device inwhich the set of calibration data is stored. The memory storage devicemay be an EEPROM. In any of the preceding embodiments, the calibrationdata comprises a pressure-deflection relationship for the resilientsheath.

Any of the preceding embodiments may include a catheter forming thehousing. In some embodiments, the optical fiber is adhered to thehousing.

Any of the preceding embodiments may include a rotational mechanismconfigured to rotate the probe to generate an OCT image. Any of thepreceding embodiments may include a mirror near the opening, the mirrorconfigured to reflect optical radiation from the fiber to the sheath.

In any of the preceding embodiments, the optical fiber comprises a coreproviding a common path for optical radiation reflected from a referenceand the sheath.

In any of the preceding embodiments, the receiving electronics includesa detector.

Further embodiments provide for methods of determining pressure in ablood vessel. These methods include transmitting light from a sourcethrough an optical fiber; transmitting the light from the optical fiberto a deflected surface of an elastic membrane, wherein the elasticmembrane is moveable in response to pressure exerted against themembrane; transmitting reflected or scattered light from the elasticmembrane to a detector; receiving the reflected or scattered light atthe detector; generating a intravascular pressure measurement from thelight received by the detector from the elastic membrane.

In any of the preceding embodiments, the generating step includescomputing the pressure measurement based on a membrane deflectiondistance between the membrane surface and the optical fiber. In any ofthe preceding embodiments, the deflection distance is indicated by anintensity value and a pixel depth value for the light received by thedetector from the elastic membrane.

In any of the preceding embodiments, the generating step includestransmitting data from the detector to a processor, wherein the datarepresents an interference signal resulting from the interaction of areference reflected light and a membrane scattered or reflected light,the processor computing an intravascular pressure based on theinterference signal.

In any of the preceding embodiments, the generating step includescomputing a path length from the optical fiber and the deflected surfaceof the membrane, the computation based on a difference in phase, time orfrequency between a reference reflected light and a membrane scatteredor reflected light.

Any of the preceding embodiments may include calculating a fractionalflow reserve for the vessel. Any of the preceding embodiments mayinclude calculating a first pressure at a first location and a secondpressure at a second location.

Further embodiments provide for methods of determining pressure in avessel with an OCT catheter. These methods include advancing an opticalfiber through a lumen of the catheter; transmitting light from a sourcethrough an optical fiber; transmitting the light from the optical fiberto a flexible elastic membrane on the catheter, wherein the elasticmembrane deflects toward the fiber under pressure; transmittingreflected or scattered light from the elastic membrane to a detector;receiving the reflected or scattered light at the detector; generatingan intravascular pressure measurement based on the light received by thedetector from the elastic membrane.

Any of the preceding embodiments may include computing the pressuremeasurement based on a membrane deflection distance. Any of thepreceding embodiments may include generating an OCT image by rotating aportion of the catheter.

Further embodiments describe an OCT pressure sensing device including anelongate body; a central lumen extending within the elongate body from aproximal end of the elongate body to a distal end of the elongate body;a rotatable tip at the distal end of the elongate body and configured torotate relative to the elongate body, the rotatable tip having an openacross which sits an elastic membrane, the membrane adapted to deflectin response to a pressure exerted against an outer surface of themembrane; and an optical fiber coupled with the rotatable tip andconfigured to rotate therewith.

In any of the preceding embodiments, the optical fiber is an OCT imagingsensor. In any of the preceding embodiments, the optical fiber andelastic membrane are adapted to measure pressure exerted against thedevice. In any of the preceding embodiments, the optical fiber andelastic membrane measure pressure while the rotational position of thedevice is relatively fixed.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe claims that follow. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1 illustrates a vessel lumen with a first and second pressure.

FIG. 2 is a schematic diagram of an interferometer.

FIG. 3 is a schematic representation of an OCT catheter.

FIG. 4 schematically shows a general optical pressure sensor assembly.

FIG. 5 illustrates the deflectable membrane and an optical fiber in anoptical pressure sensor assembly.

FIG. 6 shows the optical pressure sensor assembly of FIG. 5 with adeflected membrane.

FIG. 7 is a schematic representation of signal intensity and depthvalues for the assembly in FIG. 5 .

FIG. 8 is a schematic representation of signal intensity and depthvalues for the assembly in FIG. 6 .

FIG. 9 is a schematic representation of pressure to depth values for acalibrated optical pressure sensor assembly.

FIG. 10 shows an imaging system that can be interchangeably coupled toan optical pressure sensor assembly and other catheter devices.

FIG. 11 is a perspective view of an optical pressure sensor assembly.

FIG. 12 is a top view of the assembly of FIG. 11 showing the opening inthe housing.

FIG. 13 is a cross-section view of the assembly of FIG. 11 .

FIG. 14 is a cross-section view of an optical pressure sensor assemblyaccording to some embodiments.

FIG. 15 shows a vessel with an optical pressure sensor assemblymeasuring pressure at two locations.

FIG. 16 shows a catheter device with a removable optical pressure wire.

FIG. 17 shows the distal end of the catheter device in FIG. 16 .

FIG. 18 shows the proximal end of the catheter device in FIG. 16 havingan optical connector.

FIG. 19 is a cross-section view of a pressure wire assembly having anoptical connector at the proximal end of the fiber.

FIG. 20 is a schematic representation of exemplary optical connectors.

FIG. 21 is a schematic representation of alternative optical connectors.

FIGS. 22A-D show a pressure sensor assembly with a front-firing opticalfiber.

FIG. 23 schematically shows a pressure sensor assembly in use with animaging system (e.g. OCT system).

DETAILED DESCRIPTION

Embodiments described herein provide for optical pressure sensorassemblies that utilize the basic framework of an imaging system toprovide pressure measurements. Although any suitable optical or imagingmodality can be used with the contemplated invention(s), opticalcoherence tomography (OCT) is described as an illustrative example ofhow the invention is compatible with an imaging system. As such, ageneral overview of OCT is provided below, followed by a description ofthe optical pressure sensor assemblies that can be used with OCT orother imaging systems. It is to be appreciated, that the OCT discussionis for illustration purposes and not limiting the invention to anyspecific imaging modality.

I. OCT System General Overview

OCT has been proposed as one technique that may be particularly helpfulfor imaging regions of tissue, including within a body lumen such as ablood vessel. At a basic level, OCT relies on the fact that lighttraveling from a source and scattering from more distant objects takeslonger to travel back than light scattering from nearby objects. Due tothe wave nature of light, very small timing differences caused by lightsignals traveling different distances on the micron scale can causeconstructive or destructive interference with reference light signals.OCT systems measure the resulting interference to obtain an image of thetarget. A typical OCT system requires one or more interferometers todistinguish the signal from the applied light.

Referring to FIG. 2 , a general OCT device includes a target arm and areference arm to generate a reference signal. In order to provide theinterference reference signal, the OCT device will split an illuminatinglight signal from the source in two equal or unequal parts, send part ofthe illuminating light to the target of interest through one targetoptical “target arm” and send the other part of the illuminating lightdown a separate reference arm. Light from the separate reference armreflects off of a mirror, and then returns and interferes with thescattered light that is returning from the target optical arm afterbouncing off of the target. In a traditional OCT device, the referencearm length is engineered to be exactly the same length as the target armso that the interference effect is maximized. The resulting interferencebetween the two beams creates interference effects known as fringes thatcan be used to measure the relative reflectivity of various layers ofthe target. Using this information, an image of the object can begenerated.

In addition, most known OCT systems, when applied to catheters, includea fiber that is rotated (often at high rates) within the catheter inorder to scan around a lumen. During a medical procedure, such acardiovascular catheter is typically removed from the factory sterilecontainer. The proximal end of the catheter is connected to equipmentneeded to control the catheter (which in this case would also includethe link to the OCT engine used to drive any OCT optical fiber in thecatheter), and the distal tip is immediately inserted into the patient'sbody. The catheter is then discarded once the procedure is complete.

FIG. 3 provides a general illustration of a cardiovascular catheter thatutilizes OCT for imaging. A common-path OCT system 100 includes a lasersource 102, such as a swept frequency light source. An optical fiber 104transfers optical radiation from the laser source 102 to the target 114.In some embodiments, the optical fiber 104 is a side-firing fiber thatemits optical radiation from an angle relative to the longitudinal axisof the fiber 104. For example, the fiber 104 may transmit light at 90degrees to the longitudinal axis. In other embodiments, the opticalfiber may transmit in a straight path to a mirror 180 that reflects thetransmitted light to the target 114. Some of the light beam that exitsthe optical fiber 104 will encounter the target 114 and be reflected orscattered by the target 114. Some of this reflected or scattered lightwill, in turn, reenter the tip of the optical fiber 104 and travel backdown the fiber 104 in the opposite direction.

A Faraday isolation device 112, such as a Faraday Effect opticalcirculator, can be used to separate the paths of the outgoing lightsource signal and the target and reference signals returning from thedistal end of the fiber. The reflected or scattered target light and thereflected reference light from the fiber can travel back to a detector110 located at the proximal end of the optical fiber 104.

Because the reflected or scattered target light in the OCT system 100travels a longer distance than the reflected reference light, thereflected or scattered target light can be displaced by frequency, phaseand or time with respect to the reference beam. For example, ifswept-source radiation is used, then the light from the target will bedisplaced in frequency. The difference in displacement in phase, time orfrequency between the reflected or scattered target light and thereference light can be used to derive the path length difference betweenthe end of the optical fiber tip and the light reflecting or lightscattering region of the target. In the case of swept source OCT, thedisplacement is encoded as a beat frequency heterodyned on the carrierreference beam. Additionally, a computer or other processor may receivedata corresponding to the reflected light in order to generate images ofthe target or to perform computations with the received data.

The laser source 102 can operate at a wavelength within the biologicalwindow where both hemoglobin and water do not strongly absorb the light,i.e. between 800 nm and 1.5 μm. For example, the laser source 102 canoperate at a center wavelength of between about 1300 nm and 1400 nm,such as about 1310 nm to 1340 nm. In various embodiments, where theimaging modality is not OCT, the light source does not have to operatein a biological window, rather any wavelength of light can be used toprovide light to the optical pressure assemblies described.

Additionally, the optical fiber 104 can be a single mode optical fiberfor the ranges of wavelengths provided by the laser source 102. Theoptical fiber may have a cut-off less than 1260 nm and have single modeperformance between 1270 and 1380 nm (and be manufactured compatiblewith SMF-28 standards).

II. Optical Pressure Sensor Assembly

As described above, one of the challenges for intravascular pressuremeasurement is the need for a pressure sensor that avoids the drawbacksof electrical interference such as drift, which affects the accuracy andreliability of electrical pressure sensors. To address this need,embodiments described provide for an optically-based pressure sensorthat uses interferometry to determine intravascular pressure. Inparticular, the contemplated pressure sensor uses light reflected orscattered from an elastic membrane deflected by vessel pressure todetermine blood pressure at target vessel locations. Because themechanism is light-based, electrical disturbances like drift areavoided.

Generally, the pressure sensor assembly includes an elongate body suchas an elongate housing or catheter. The elongate body is hollow orincludes a lumen through which an optic fiber extends. The body includesan opening or hole, which is covered by an elastic membrane. The elasticmembrane may only cover the hole or, alternatively, the elastic membranemay extend around the body to cover the hole as well as other portionsof the body. The elastic membrane is adapted to move, deflect, or changeshape in response to pressure exerted against the membrane.

In operation, positive intravascular fluid pressure pushes against asurface of the membrane exposed to the intravascular environment. Thepositive fluid pressure depresses or deflects the membrane toward aninterior of the elongate body such as toward a central longitudinal axisof the body.

To provide optical pressure sensing, the optical fiber inside the bodyhas a light emitting end aligned with the elastic membrane to allow thetransmission of light from the fiber end to the elastic membrane. Alight beam emitting from the fiber end will encounter the elasticmembrane, which results in absorption, scattering, and reflection. Someof the reflected or scattered light will re-enter the light emitting endof the fiber to travel back down the fiber toward a proximal end of thefiber. The interaction of a reference light and the reflected/scatteredlight from the membrane is detected and used to determine the membranedeflection distance, which is used to compute the intravascular pressureexerted on the membrane.

Advantageously, the optical pressure sensors/assemblies can be used asstandalone devices that are fed into a patient's vasculature to measureblood pressure at specific vessel locations. The pressure sensorassemblies may be used with an imaging system that provides a lightsource and electronics for detecting reflected/scattered light andcomputing pressure measurements.

Additionally, the described optical pressure sensor/assemblies arecompatible for use with the existing architecture of intravasculardevices (without or without imaging capability). In some embodiments,the pressure sensor assembly can be dimensioned to fit inside a lumen,such as a guidewire lumen, of an intravascular device. The pressuresensor assembly is advanced through the device lumen into a patient'svasculature. Once a pressure measuring end of the assembly is exposed inthe vessel, pressure readings can be taken for that location. Where anintravascular device includes an optical interferometry system such asOCT, the pressure sensor assembly may use the existing light source andother components of the imaging system to measure and compute pressure.Alternatively, where the intravascular device is not equipped forimaging, the pressure sensor assembly may include an optical/imagingsystem for providing light, detecting reflected/scattered light, andcomputing intravascular pressure. In further embodiments, the opticalpressure sensor assembly also functions as a guidewire.

In another variation, the pressure sensor assembly may be integratedinto an intravascular device such that the device has built-in pressuremeasuring capabilities. For example, the pressure sensor assemblycomponents can be integrated with an OCT imaging and occlusion-crossingcatheter device, such as those described in U.S. patent application Ser.No. 13/433,049, titled “OCCLUSION-CROSSING DEVICES, IMAGING, ANDATHERECTOMY DEVICES,” filed Mar. 28, 2012. The integrated device mayinclude a catheter having a tip portion with an opening covered by anelastic membrane. An optical fiber resides within the body of thecatheter with a light emitting end aligned with the opening andmembrane. In one mode, the integrated device measures pressure while thedevice is rotationally fixed. In another mode, the integrated devicegenerates OCT images by rotating the tip portion. In such cases, theoptic fiber serves both as a pressure sensor and an OCT imaging sensor.Additionally, the integrated device may operate as part of an integratedsystem having components to control the integrated device, computepressure, and generate OCT images.

Referring now to FIGS. 4-10 , these illustrate schematically the generalassembly components and methods by which the optical pressure sensorassembly measures intravascular pressure. FIG. 4 shows a generalpressure sensor assembly 202 that is connected to an optical/imagingsystem 200. The imaging system 200 includes a light source 202 and adetector 206, and can be an OCT imaging system that is used tointerchangeably generate images of the vascular lumen and measureintravascular pressure.

The pressure sensor assembly 202 includes an optical fiber 212 that iscoupled to the imaging system 200. The optical fiber 212 is surroundedby a housing 210 that includes an opening 209 at a distal tip of thehousing. The opening 209 is covered by an elastic membrane 208 that candeflect or move in response to pressure from the intravascularenvironment.

Any suitable membrane shape is acceptable provided that the membraneshape distorts to decrease the distance between the membrane and thefiber when the membrane experiences pressure. In some embodiments, themembrane is configured to adopt a concave shape or meniscus shape whenpressure is exerted against a surface of the membrane, such as a topsurface exposed to a surrounding intravascular environment. In a neutralnon-deflected state, the membrane can have any shape including arelatively straight or slightly curved profile. In various embodiments,the membrane may be adapted to measure pressure between 40 mmHg to 250mmHg or 60 mmHg to 200 mmHg.

As shown in FIG. 4 , a distal end or light emitting end of the fiber 212is aligned with the opening and membrane such that the fiber distal endis positioned near or below the membrane. Where a side-firing fiber isused, light emitted from the distal end of the fiber is directed towardthe membrane and opening. In other variations, a mirror 216 is includedin the distal tip to reflect light towards the elastic membrane 208. Amirror 216 may be used to redirect light from a front-firing fiber tothe membrane 208.

In practice, the light source 204 provides optical radiation/light fortransmission through the optical fiber 212. At the light emitting fiberend, some of the transmitted light will be reflected back from thedistal tip or the circumference at the distal tip (in case of aside-firing fiber) of the fiber, hence forth referred as referencesurface to create a first signal that serves as a reference signal forthe pressure sensor assembly.

In some embodiments, the reference reflected light or reference signalis created by a common-path OCT system 100 shown in FIG. 3 . The indexof refraction of the interface medium 106 is different than the index ofrefraction of the distal edge of the optical fiber 104. Part of thelight will exit the optical fiber 104 while part of the light will bereflected back from the distal end of the optical fiber 104, creating areference reflection called a Fresnel reflection. In some cases, a GRINfiber can be used to generate the Fresnel reflection.

In the common-path OCT system the optical fiber has a core providing acommon path for optical radiation reflected from a reference interfaceand a target. The core has a first refractive index, n₁. The distal tipof the optical fiber is surrounded by interface medium such as anadhesive. The interface medium has a second refractive index n₂. Part ofthe light that exits from the distal tip of the fiber is reflected backdue to Fresnel reflection. When the incident and thus the reflectedlight are perpendicular intensity of reflection can be given by theFresnel equation shown below.

$R = ( \frac{n_{1} - n_{2}}{n_{1} + n_{2}} )^{2}$

For common path OCT the first refractive index and the second refractiveindex are mismatched such that the reference reflection lies between −28dB and −38 dB. This ensures optimal operation of the receivingelectronics of the common path OCT system are described in U.S. patentapplication Ser. No. 12/790,703, filed May 28, 2010 and titled “OPTICALCOHERENCE TOMOGRAPHY FOR BIOLOGICAL IMAGING”, Publication No.US-2010-0305452-A1.

Some examples of the adhesive used as an interface medium are MasterbondEP42HT-2, EpoTek OG127-4 or OG116, produced by Epoxy Technology,Billerica Mass. and UV curable photonics adhesive OP-4-20658, producedby Dymax corporation, Torrington Conn.

In addition to the reflected reference light described above, some ofthe light exiting the fiber 212 encounters a surface or region of theelastic membrane 208. Some of this light will be reflected or scatteredby the elastic membrane and re-enter the fiber 212, traveling down thefiber 212 in the opposite direction to generate a second signal, whereinthe second signal represents light reflected/scattered by the membrane.

As shown in FIG. 4 , the elastic membrane is separated from the opticfiber by a variable distance D. Unlike the reference reflected light,light reflected or scattered from the membrane must cross distance D(i.e. light pathway length) between the fiber and the membrane. Thisresults in differences in the wave properties between the firstreference signal and the second signal generated from the membrane. Forexample, the first and second signals may differ in phase, time, and/orfrequency.

In general, the housing may be sealed so that the pressure inside thehousing is known and/or constant. The tip of the fiber optic from whichlight is emitted and received may be fixed within the housing, forexample, to a wall of the housing that is opposite to themembrane-covered opening. In some variations the housing is sealedcompletely, with a known pressure, which may allow a pressuremeasurement relative to the known pressure. In some variations theinterior of the housing is open to atmosphere pressure at the proximalend of the elongate device (e.g., near the light source), providingpressure relative to external pressure.

Moreover, an interference signal is generated from the interaction ofthe first and second signals. As described, the first reference signalis generated at the distal end of the fiber. This is also where thesecond signal from the membrane re-enters the fiber. When the twosignals meet, an interference signal is generated. The resultinginterference signal from the reference reflection and the back-scatteredlight from elastic membrane is displaced in phase, time or frequencywhich can be measured to find precise distance D between the end of theoptical fiber tip, which is stationary with respect to the housing, andthe deflected membrane. Referring to FIGS. 5-6 , the distances betweenthe elastic membrane 208 and the fiber 212 are shown for a neutral stateelastic membrane (FIG. 5 ) and a deflected elastic membrane (FIG. 6 ).Although FIG. 5 shows the membrane deflected, in some variations themembrane may be non-deflected (e.g., smooth across the opening into thehousing) or may bulge outward (e.g., housing pressure greater thanexternal pressure). In FIG. 5 , the distances D1 and D2 indicate theneutral or non-deflected pathway lengths between the optical fiber 212and the elastic membrane 208. D1 and D2 are shown measured at differentpoints (laterally) along the surface of the membrane; in practice D1 andD2 may be measured from the same portion of membrane. The elasticmembrane 208 has two surfaces from which light can scatter or reflect.D1 is the distance between reference surface on the fiber and 212 thebottom surface of the membrane 208. D2 is the distance between thereference surface on the fiber 212 and the top surface of the membrane208. Although shown as having D1 and D2 from two surfaces, the pressuresensor assembly may only utilize the distance value for one of thesurfaces as the thickness between the surfaces may stay relativelyconstant. The non-deflected state in FIG. 5 may serve as an initialreference configuration to which deflected orientations are compared.

FIG. 6 shows an example of a deflected membrane 208. In the deflectedorientation, the elastic membrane 208 has a distance D3 and D4 betweenthe reference surface on the fiber and the bottom and top surfacesrespectively. As shown, D3 is less than D1 and D4 is less than D2. Thischange in distance is notated generally as Δy. Accordingly, Δy indicatesthe amount of deflection or membrane deflection distance experienced bythe elastic membrane 208. In some embodiments, the deflection amount Δyis proportional to the force exerted on the membrane to deflect themembrane. Where force is intravascular pressure, the membrane deflectiondistance can be used to calculate the pressure at the specific vessellocation. For example, the pressure sensor assembly 202 can becalibrated such that the pressure per deflection distance relationshipis known and can be used to compute pressure once Δy is determined bythe imaging system 200. In some variations, the intravascular pressureis correlated to the difference between a first and secondfiber-membrane distance, Δy. In other embodiments, a single distancebetween the fiber and the membrane is sufficient to determine pressure(e.g. D3 or D4 alone).

In some embodiments, one method for determining the distance D betweenthe membrane and the light-emitting end of the optic fiber includesgenerating an interference signal as described above. As discussed,light is transmitted from the distal end of the fiber. Some of thislight encounters an interface medium to generate a Fresnel referencereflection that provides a first reference signal. Additionally, some ofthe transmitted light passes through the interface medium and encountersthe deflected surface of the membrane to reflect or scatter off regionsof the deflected surface. Some of the scattered/reflected light willre-enter the optic fiber to form a second signal.

Because the reflected or scattered light (second signal) from themembrane travels a longer distance than the reflected reference light,the reflected or scattered target light can be displaced by frequency,phase and or time with respect to the reference beam. For example, ifswept-source radiation is used, then the light from the membrane will bedisplaced in frequency. The difference in displacement in phase, time orfrequency between the reflected or scattered target light and thereference light can be used to derive the path length difference Dbetween the end of the optical fiber tip and the light reflecting orlight scattering region of the membrane. In the case of swept sourceOCT, the displacement is encoded as a beat frequency heterodyned on thecarrier reference beam, this creates the interference signal.

A detector, processor, controller, or other suitable electronic receivesthe interference signal and calculates the distance D based on thesignal properties. For example, the greater the distance, the higher thebeat frequency.

Continuing with the above example, once the distance D is known, thiscan compared with a non-deflected distance Do for the membrane. Adeflection distance Δy can be calculated from the deflected light pathlength D and non-deflected light path length.

Finally, pressure exerted to deflect the membrane can be computed bycomparing the deflection distance Δy to a predetermineddeflection-to-pressure relationship or rate for the membrane. Forexample, where the Δy is 60 microns and the deflection-pressure rate is10 microns per 20 mmHg of pressure, the pressure is 120 mmHg. In someembodiments, the pressure sensor assembly includes a storage devicestoring the deflection-to-pressure rate for the assembly. The storagedevice may be on the assembly, such as on the housing, and is accessibleby a processor, controller, or other electronics performing the pressurecalculation.

As described in greater detail below, any appropriate membrane material,including materials having different deflection-to-pressure rates may beused. Different thicknesses of materials may also be used. In somevariations, the housing may include multiple windows having multipledeflection-to-pressure rates and therefore different sensitivities orpressure ranges (which may overlap); each of these may be monitored orpolled by the same or different optical fibers. Thus, multiple opticalfibers may be used, or a single optical fiber that can be directed todifferent membrane-covered windows (e.g. by sliding axially within thehousing, by rotating with the housing, etc.).

Another related method for computing pressure is schematically shown inFIGS. 7-9 . FIGS. 7-8 show the relationship between signal intensity indB vs. pixel number depth. At the non-deflected position or a firstposition in the vessel, the two peaks indicate the reflected/scatteredlight received by the fiber 212 in FIG. 4 . The first peak at about adepth of 150 indicates the first distance D1 (bottom surface) which isat a closer in depth than D2 (top surface) to the fiber 212. FIG. 8shows the first and second peaks translated toward the y-axis for thedeflected membrane. This is expected as the depth for the deflectedmembrane should be less than that of the non-deflected membrane as thedeflected membrane is closer to the fiber and the light pathway lengthsbetween the membrane and the fiber are shorter. The difference Δxbetween the peaks (X1−X2) is proportional to the pressure applied todeflect the membrane. As such the difference in D1 and D3 depth for thefirst peak can be used to compute the pressure exerted on the membrane.This may be achieved by comparing the Δx value to a pressure-deflectioncurve or relationship.

This pressure-deflection relationship can be predetermined for apressure sensor assembly. This relationship may be stored as calibrationinformation for the assembly. The calibration information andrelationship may be stored on the assembly by way of a storage devicesuch as Electrically Erasable Programmable Read-Only Memory (EEPROM)whereby a processor can access calibration information to determinemeasured pressure. FIG. 9 shows a graphical representation correlatingblood pressure with the deflection of the membrane 208.

As can be appreciated, the optical pressure sensor assembly maycommunicate with a controller, processor, detector, or any otherelectronics. These electronics may receive data or signals regarding thelight received in the optic fiber. These electronics may also beconfigured to carry out any of the calculations and computationsdescribed. Additionally, these electronics may also generate images suchas OCT images.

Referring to FIGS. 11-14 , additional details regarding the componentsof the pressure sensing assembly are described. FIG. 11 shows an opticalpressure sensor assembly for use with an optical imaging system. Theoptical pressure sensor assembly 400 includes an elongate body having ahousing 402 and a covering 404 such as a hypotube. A distal tip of thehousing 402 includes an opening 414 and an elastic membrane 408positioned at the opening. An optical fiber resides within a lumen ofthe elongate body with a distal end 412 of the fiber 410 positioned nearthe opening 414 and elastic membrane 408. The distal tip of the fiber iscompletely encapsulated within an epoxy to generate the referencereflection (FIG. 14 ).

As shown, the elastic membrane 408 covers the opening 414. The material406 for the elastic membrane 408 surrounds and encircles acircumferential portion of the housing 402. In other variations, theelastic membrane covers only the opening 414 without substantiallyextending around the housing. In additional embodiments, the elasticmembrane is formed by inserting the housing 402 through heat shrinktubing and shrinking the tubing to cover the opening 414 and an outersurface of the housing. The heat shrink tubing may also be applied tocover the covering 404.

Any suitable material may be used for the elastic membrane 408 includingbiocompatible polymers such as FEP (fluorinated ethylene propylene),Tecothane®, and PET. In general, the membrane can be made from anelastic or resilient material (e.g. cross-linked polymer) that canrecover from deflection induced by intravascular pressures. In someembodiments, the membrane recover from deflection by intravascularpressures between about 40 mmHg to about 250 mmHg Additionally, anymaterial that exhibits measurable deflection when pressure or force isexerted against the membrane can be used for the membrane. Because thepressure force will be in a range associated with blood pressure, themembrane may demonstrate a spring force or resilience that is suitablefor measuring pressures between about 40 to about 250 mmHg Additionally,the elastic membrane may have a thickness between about 10 microns toabout 50 microns. Although described as an elastic membrane, themembrane may also be any suitable movable element such as a flexible orcompliant diaphragm, sheath, meniscus, spring or other component thatmoves in response to blood pressure.

In some embodiments, the elastic membrane 408 forms a crescent-shape ormeniscus shape across the opening 414 when deflected. The deflectedelastic membrane 408 may dip or curve slightly to form a concave topsurface and a convex bottom surface across the opening 414. Any suitablemembrane shape is acceptable provided that the membrane shape distortsto decrease the distance between the membrane and the fiber when themembrane experiences pressure. In some embodiments, the membrane isconfigured to adopt a concave shape or meniscus shape when pressure isexerted against a surface of the membrane, such as a top surface exposedto a surrounding intravascular environment. In a neutral non-deflectedstate, membrane can have any shape including a relatively straight orslightly curved profile.

The opening 414 is generally sized to permit an elastic membrane to sitover the opening while supported by the housing 402 structure. Theopening 414 may be any suitable size for achieving this purposeincluding between about 100-500 microns, 200-400 microns, or 100-200microns. Generally, the opening is sized to allow a light beam to exitthe opening. As shown, the opening is formed on the housing 402 throughthe side wall of the housing 402. Additionally, the opening can have acircular, oval, and/or elliptical shape. However, the opening is notlimited to these shapes.

As shown in FIG. 13 , the opening 414 is positioned at about 90 degreesrelative to a central longitudinal axis through the housing 402. This isparticularly useful where OCT images can be generated by the pressuresensor assembly when the housing 402 is rotated within a vessel lumen.However, the opening is not limited to a side position. The opening canbe placed at the end of the distal tip on the central longitudinal axisof the housing. In such cases, the fiber may transmit and receive lightthrough a distal end of the fiber facing the opening. Such variationscan be used with non-OCT imaging systems that employ interferometry.

FIG. 13 shows the optical fiber 410 with distal end cleaved at an anglesuch as 45 degrees and the end surface is polished and coated withreflective material such as Gold. The angle polish/cleave with goldcoating allows the light to be reflected at an angle such as 90 degreesto the longitudinal axis of the fiber. The distal end of the fiber 412is placed near the opening 414. The optical fiber may reside in acentral or off-axis lumen through the housing. The fiber may be adheredor otherwise mechanically secured to the assembly. In some embodiments,an interface medium such as an adhesive 416 is placed at the firing endof the fiber to create a Fresnel reference reflection as described indetail above.

Additionally, the optical fiber 410 can be a single mode optical fiberfor the ranges of wavelengths provided by the light source. The opticalfiber may have a cut-off less than 1260 nm and have single modeperformance between 1270 and 1380 nm (and be manufactured compatiblewith SMF-28 standards).

In yet another embodiment, a front-firing fiber, such as optical fibercleaved between 0 and 2 degrees may be used in conjunction with a mirrorfor reflecting light through from the opening on the side of thehousing. FIGS. 22A-D show an exemplary optical pressure sensor assembly2500 having a hollow elongate body 2502 with a distal tip 2504. Thedistal tip 2504 including an opening 2508 covered by a resilient sheath2510. The resilient sheath is adapted to distort or deflect whenintravascular pressure is exerted against the sheath.

Referring to the cross-sectional views in FIGS. 22C-D, an optical fiber2512 resides within a lumen inside the elongate body. The optical fiberhas a front-firing distal end 2511 that emits light to a mirror 2514.The mirror 2514 is positioned to reflect light at an angle towards themembrane. Additionally, the mirror 2514 directs light that isreflected/scattered back from the membrane into the distal end 2511 ofthe optic fiber 2511.

Furthermore, to use the pressure sensor assembly with an optical/imagingsystem, the assembly may include optical and electrical connectors totransfer light and power from the imaging system to the assembly.

In operation, the optical pressure sensor assembly 400 measures bloodpressure by detecting reflected/scattered light from the elasticmembrane and computing the distance between the deflected elasticmembrane and the distal tip of the optical fiber. Referring to FIG. 15 ,in the un-deflected or neutral state, the elastic membrane provides areference distance 502 between the membrane and the firing end 411 ofthe optical fiber 410. Increased pressure P1 exerted against the outsidesurface of the elastic membrane, which is in direct contact with blood,pushes down against the elastic membrane to deflect and distort themembrane towards the reference surface on the optical fiber 410. Thechanged distance between the elastic membrane and the reference surfaceis proportional to blood pressure.

In practice, pressure measurements at two locations are taken forcomparison to determine the pressure ratio or gradient caused by anocclusion. In some cases, a measurement is taken on either side of anocclusion. FIG. 15 shows a first pressure P1 taken at a first locationand a second pressure P2 taken at a second location on the other side ofthe occlusion. Alternatively, the first and second measurements may betaken on the same side of the occlusion. The first measurement may betaken to determine a baseline pressure for the patient and the secondmeasurement is taken near or at the occlusion to determine the increasedpressure caused by the blockage. The baseline pressure is compared tothe second measurement to compute a ratio or gradient.

As discussed, a processor, computer, or other electronic component maybe used to calculate pressure. The processor may compute the measureddeflection with reference or calibration data for the pressure sensorassembly. Reference or calibration data for the assembly can include thepressure-membrane deflection relationship for the specific assembly.This data can be provided in a memory storage device such as EEPROM thatis accessible by a processor or computer configured for computing themeasured pressure(s). The memory storage device may be included in thebody of the assembly, e.g. on the housing, for easy access by aprocessor.

Because the optical pressure sensor assembly is designed to beintroduced into and advanced through a patient's vasculature, theassembly may employ a catheter as the main body for containing thedescribed components. The catheter can be dimensioned to fit withinvessels of the body, such as blood vessels. For example, the catheterscan be configured to be placed within the peripheral blood vessels.Thus, the catheters can have an outer diameter of less than 0.1 inch,such as less than 0.09 inches, such as less than or equal to 0.08inches.

Advantageously, as mentioned, the pressure sensor assemblies describedcan be used as a standalone device, as a complementary device for anexisting intravascular device (e.g. occlusion-crossing or atherectomycatheters), or as part of an integrated intravascular device withpressure sensing capabilities. For example, FIG. 10 provides an exampleof a general OCT system 300 that can be used with these variousembodiments. The OCT system 300 includes a console 304 that may includea computer or processor, light source, and display 306. The display maydisplay OCT images or pressure values. The console 304 is in opticaland/or electrical communication with a connector 302. In some cases, theconsole is in communication with a series of connectors 302 a-b. Theconnectors 302 a-b are adapted to couple to a corresponding orcomplementary connector on a pressure sensor assembly or intravasculardevice.

As shown, the OCT system can be used with the standalone opticalpressure sensor assembly 310. The optical pressure sensor assembly maybe any of the embodiments described; however, in FIG. 10 , the pressuresensor assembly is configured for use with the OCT system. The opticalpressure sensor assembly 310 can be coupled to one of the connectors 302a-b to receive power or light. Once connected to the light source, theoptical pressure sensor assembly 310 can be used to measureintravascular pressure. This can be achieved by exposing a sensingportion of the assembly (e.g. distal tip having a deflectable membraneand optic fiber) to fluid pressure in a patient's vasculature andcalculating the pressure based on optical properties of light scatteredor reflected in the sensing portion. The OCT console (or separatecontroller) can be used to compute the intravascular pressure.

Alternatively, the optical pressure sensor assembly 310 may be used withthe occlusion-crossing and OCT imaging catheter device 308. The OCTdevice 308 includes connectors 303 for optically and electricallycoupling the device 304 to the controller 304. Although havingocclusion-crossing or OCT capabilities, the catheter 308 is not equippedfor pressure sensing. Because the OCT system has a light source,detector, applicable electronics, processors, etc., the imagingcomponents of the OCT system can be used with the pressure sensorassembly 310 described to generate pressure measurements once thecatheter 310 is advanced into the patient's vessel.

FIGS. 16-18 illustrate an example of this embodiment. Referring to FIGS.16-18 , an OCT imaging and occlusion-crossing device 1300 is shown. Thedevice 1300 includes a catheter or flexible hollow shaft 1302 with adistal tip 1301. The distal tip 1301 includes an OCT imaging sensor 1330and a cutter 1332 for removing an occlusion. The catheter 1302 includesa lumen extending from a proximal end through the distal tip 1301 of thecatheter. The lumen allows the passage of a guide wire or the opticalpressure sensor assembly 1304 through the catheter 1302. The opticalpressure sensor assembly 1304 is dimensioned to pass through theexisting lumen of the catheter 1302.

In operation, once the catheter 1302 is placed inside the patient's bodyusing a guide wire the guide wire can be removed to insert the opticalpressure sensor assembly 1304 through the catheter 1302. The pressuresensor assembly 1304 moves through the catheter tip 1301 to expose asensing portion 1340 of the assembly 1304 to the surroundingintravascular environment. Alternatively, in some variations, thepressure sensor assembly 1304 also functions as a guide wire, in whichcase it eliminates the need for a separate guide wire.

As shown in FIGS. 16-18 , the assembly 1304 includes an elongate hollowbody 1346 with a distal portion 1304 having a hole covered by adeflectable membrane 1344. An optic fiber resides in the elongate hollowbody 1346 with a distal firing end positioned near the membrane 1344.The distal firing end of the fiber is aligned and orientated such thatemitted light can encounter the membrane 1344 and reflected/scatteredlight from the membrane can re-enter the fiber for detection byreceiving electronics connected to the optical pressure sensor assembly.In some cases, the OCT console shown in FIG. 10 functions as receivingelectronics to compute a pressure value based on the light received inthe fiber from the membrane.

Additionally, the proximal end of the pressure sensor assembly 1348 mayinclude a first optical connector for coupling to a second connector1308. The second connector 1308 may be fused to another optic fiber inoptical communication with a light source. The proximal end of theassembly may also connect to an OCT imaging console for pressuresensing.

FIG. 23 schematically illustrates an OCT system 2600 for use with anoptical pressure sensor assembly 2608 that can be passed through a lumenof an intravascular device 2603. The OCT and pressure sensing system2600 includes an OCT device 2602 having a hollow shaft 2606 defining aninternal lumen. The OCT device 2602 includes an actuator or handleportion 2604 for controlling the device 2603. An optical pressure sensorassembly 2608 extends through the lumen of the device 2603 with apressure sensing portion residing distal of the distal end of the device2603.

The proximal end of the pressure sensor assembly includes an opticalconnector 2610 for coupling to a system connector 2612 that is incommunication with a console 2620 via line 2614. In some embodiments,the console 2620 includes an optical switch 2622 for controlling thetransmission of light between the OCT device and the optical pressuresensor assembly. In one mode, the optical switch 2622 connects theconsole 2620 (and light source) to the device 2603 via connectors 2605and 2607. In another mode, the optical switch 2622 connects the console2620 (and light source) to the pressure sensor assembly.

Referring again to FIG. 10 , in another aspect, embodiments provided foran integrated intravascular device 312 having a built-in opticalpressure sensing assembly. OCT/occlusion-crossing catheter 312 has (1)OCT imaging; (2) occlusion-crossing; and (3) pressure sensing features.The integrated intravascular device 312 has a catheter or elongate bodywith a central lumen extending therethrough. The catheter has arotatable tip at the distal end of the catheter. The rotatable tiphaving an opening covered by a deflectable membrane. An optic fiber sitsin the central lumen with a firing end near the opening. In someembodiments, the optic fiber is also configured to rotate with therotatable tip.

In some variations, the catheter 312 can switch between imaging andpressure measurement modes. In one operation mode, the catheter 312rotates and provides OCT images showing the vessel structure. In anothermode, the catheter 312 does not rotate (e.g. relatively fixedrotationally) and measures the intravascular pressure. In someembodiments, the same optical fiber used for OCT imaging is used forpressure measurement.

Another example of a catheter with built-in pressure sensing features isan atherectomy catheter that includes an elastic membrane and fixed orremovable optical pressure wire/fiber. The elastic membrane is movablein response to pressure. When a pressure reading is needed the catheteris connected to an imaging system that provides a light source,detector, and other receiving electronics to compute pressure based onoptical properties of light scattered or reflected by the membrane.

For any of the described embodiments, any suitable optical connector maybe used. As shown in FIG. 19 , the proximal end 2411 of the fiber 2309includes an optical connector adapted to couple the fiber to a lightsource. The light source is another optical fiber 2420 that ispresumably connected to light source (e.g. laser). The source opticalfiber 2420 includes an optical connector 2424 on a distal end forinterfacing the optical connector 2422 of the receiving fiber 2410. Anysuitable optical connectors may be used, including an element of similardiameter to a GRIN fiber for efficient coupling. Additionally, theproximal end 2411 of the fiber receiving 2410 may be cleaved (e.g. anglecleaved) and positioned to focus light from the source optical fiber2420 into the receiving optical fiber 2410.

FIGS. 20-21 show additional optical coupling variations. FIG. 20 shows aset of lenses 2440 a-b for collimating light from a first optical fiber2420 from the system to a second optical fiber 2410 in the pressuremeasuring catheter. FIG. 21 shows a similar coupling mechanism with asingle lens 2440. A GRIN lens 2433 is also located at the coupling endof the second optical fiber configured for receiving/transmitting lightto the first optical fiber.

III. Methods of Measuring Pressure with an Optical Pressure SensorAssembly

Additional details describing the methods of measuring pressure with anoptical pressure sensor assembly are provided in this section. As ageneral matter, any methods used for optical interferometry areapplicable to detecting reflected and scattered light from a referenceand a target. Typically, interferometers transmit light from a sourcethrough an optical fiber. The transmitted light is often split into twobeams where a first beam is directed to a reference structure and asecond beam is directed to a target structure. When each beam encountersa structure, the structure will reflect and/or scatter the receivedlight. Some of the reflected/scattered light will enter the opticalfiber and travel to a detector. The detector or a separate processor incommunication with the detector can use the received light to determinethe distance between the transmitting end of the optical fiber and thescatter/reflection point on the encountered structure.

As discussed above, this distance information can be used to computeintravascular pressure where distance is proportional to pressure.Optical pressure sensor assemblies include a movable membrane such as adeflectable membrane that varies in distances from the optical fiberdepending on surrounding blood pressure. The movable membrane serves asthe target structure from which transmitted light is reflected orscattered back into and received by the optical fiber. Thisreflected/scattered light is received and processed to determine thedistance between the optical fiber and the deflected membrane.

Although distance can be measured in any suitable unit, in someembodiments, the distances are presented by an intensity vs. pixel depthrelationship. As shown in FIGS. 7-8 , the pixel depths corresponding topeak intensities indicate distances between the optical fiber and themovable membrane. When deflected, the distances between the membrane andthe fiber decreases, which is indicated by a decrease in pixel depth.The change in this distance can be used to determine pressure. Forexample, a processor (or the detector) can calculate the change in Δxdistance between the peaks in FIG. 7 and FIG. 8 . The change in distanceis then compared to calibration data for the pressure sensor assembly.The calibration data can include the deflection distance to pressurerelationship for the movable membrane (see FIG. 9 ).

Alternatively, intravascular pressure may computed by determining theamount of distance that a membrane has deflected in response to pressureexerted against the membrane. In such cases, the optical pressure sensorassembly may include a baseline distance D₀ indicating a first distancebetween the membrane and the fiber without deflection from pressure. Thefirst distance is compared to a second distance D_(s) where the seconddistance is a deflected distance for the membrane under pressure.Typically, the second distance will be closer to the optic fiber as thepressure is exerted against an outer surface of the membrane to depressthe membrane toward the optic fiber. The difference (Δy) between thefirst and second distance can be computed and compared to adeflection-pressure rate or relationship for the assembly to determinethe pressure exerted to deflect the membrane.

In order to determine the value of the second distance, opticalinterferometry can be used as described. This can include the steps oftransmitting light from a source through an optical fiber, transmittingthe light from the optical fiber to a deflected surface of an elasticmembrane, and transmitting light reflected or scattered light from theelastic membrane to a detector or processor that can compute the seconddistance based on properties of the received light.

In some variations, as described, an interference signal is created fromthe interaction of a reference reflection signal and a membranereflected/scattered signal. A processor or controller etc. may be usedto determine the second distance of the deflected membrane from theproperties of the interference signal.

Once the second distance is determined, the distance difference Δy iscalculated by subtracting D_(s) from D₀. The distance difference is thencompared to a predetermined deflection distance to pressure rate orrelationship for the membrane and the pressure assembly. In someembodiments, a processor, detector, controller etc. is configured tocompute or derive pressure from the membrane-to-fiber distanceinformation.

Additionally, in other embodiments, pressure is determined withoutcalculating a distance difference Δy. Rather, a single distance detectedbetween the movable membrane and optical fiber is correlated topressure.

Furthermore, pressure may be measured multiple times at multiplelocations. For example, pressure may be measured prior to starting aprocedure to confirm that the pressure gradient or pressure ratio (FFR)satisfies a threshold value warranting the procedure. Similarly,pressure may be measured after a procedure to confirm that a vessel hasbeen adequately widened.

Additional details pertinent to the present invention, includingmaterials and manufacturing techniques, may be employed as within thelevel of those with skill in the relevant art. The same may hold truewith respect to method-based aspects of the invention in terms ofadditional acts commonly or logically employed. Also, it is contemplatedthat any optional feature of the inventive variations described may beset forth and claimed independently, or in combination with any one ormore of the features described herein. Likewise, reference to a singularitem, includes the possibility that there are plural of the same itemspresent. More specifically, as used herein and in the appended claims,the singular forms “a,” “and,” “said,” and “the” include pluralreferents unless the context clearly dictates otherwise. It is furthernoted that the claims may be drafted to exclude any optional element. Assuch, this statement is intended to serve as antecedent basis for use ofsuch exclusive terminology as “solely,” “only” and the like inconnection with the recitation of claim elements, or use of a “negative”limitation. Unless defined otherwise herein, all technical andscientific terms used herein have the same meaning as commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. The breadth of the present invention is not to be limited bythe examples described herein, but only by the plain meaning of theclaim terms employed.

When a feature or element is herein referred to as being “on” anotherfeature or element, it can be directly on the other feature or elementor intervening features and/or elements may also be present. Incontrast, when a feature or element is referred to as being “directlyon” another feature or element, there are no intervening features orelements present. It will also be understood that, when a feature orelement is referred to as being “connected”, “attached” or “coupled” toanother feature or element, it can be directly connected, attached orcoupled to the other feature or element or intervening features orelements may be present. In contrast, when a feature or element isreferred to as being “directly connected”, “directly attached” or“directly coupled” to another feature or element, there are nointervening features or elements present. Although described or shownwith respect to one embodiment, the features and elements so describedor shown can apply to other embodiments. It will also be appreciated bythose of skill in the art that references to a structure or feature thatis disposed “adjacent” another feature may have portions that overlap orunderlie the adjacent feature.

As used herein in the specification and claims, including as used in theexamples and unless otherwise expressly specified, all numbers may beread as if prefaced by the word “about” or “approximately,” even if theterm does not expressly appear. The phrase “about” or “approximately”may be used when describing magnitude and/or position to indicate thatthe value and/or position described is within a reasonable expectedrange of values and/or positions. For example, a numeric value may havea value that is +/−0.1% of the stated value (or range of values), +/−1%of the stated value (or range of values), +/−2% of the stated value (orrange of values), +/−5% of the stated value (or range of values), +/−10%of the stated value (or range of values), etc. Any numerical rangerecited herein is intended to include all sub-ranges subsumed therein.

What is claimed is:
 1. A pressure measurement system, comprising: anoptical radiation source; a pressure probe comprising: an optical fiber;a housing surrounding a portion of the optical fiber, a distal end ofthe optical fiber positioned at an opening of the housing at a first endof the housing; a resilient sheath overlaid across the opening in thehousing, the sheath adapted to deflect in response to a pressure exertedon an outer surface of the sheath, the optical fiber configured totransmit optical radiation to the sheath and receive optical radiationreflected or scattered by the sheath while the sheath is deflected; amirror in a distal tip of the housing, wherein the mirror is configuredto reflect optical radiation from the optical fiber to the sheath; andan optical connector in optical communication with the optical radiationsource; receiving electronics configured to receive the reflected orscattered optical radiation from the optical fiber; and a processorconfigured to compute a pressure value based upon the optical radiationreceived by the receiving electronics.
 2. The system of claim 1, furthercomprising a display in communication with the processor, the displayconfigured for displaying measured pressure values.
 3. The system ofclaim 1, wherein the resilient sheath is a flexible membrane adapted todeflect toward the optical fiber under positive pressure from theenvironment.
 4. The system of claim 1, wherein the resilient sheath is aflexible membrane having a convex surface facing the optical fiber whendeflected by pressure exerted on the outer surface.
 5. The system ofclaim 1, wherein the optical fiber is removable from the housing.
 6. Thesystem of claim 1, wherein the processor is configured to generate thepressure value by comparing the optical radiation received by thereceiving electronics with a set of pressure calibration data for theprobe.
 7. The system of claim 6, further comprising a memory storagedevice in which the set of calibration data is stored.
 8. The system ofclaim 7, wherein the memory storage device is an electrically erasableprogrammable read-only memory (EEPROM).
 9. The system of claim 6,wherein the calibration data comprises a pressure-deflectionrelationship for the resilient sheath.
 10. The system of claim 1,further comprising a catheter forming the housing.
 11. The system ofclaim 1, wherein the optical fiber is adhered to the housing.
 12. Thesystem of claim 1, further comprising a rotational mechanism configuredto rotate the probe to generate an OCT image.
 13. The system of claim 1,wherein the optical fiber comprises a core providing a common path foroptical radiation reflected or scattered from a reference and thesheath.
 14. The system of claim 1, wherein the receiving electronicscomprises a detector.